Incorporated in diets for domestic animals is a variety of additives. For example, it is described in Japanese Patent Laid open No. (JP-A) 58-155050 that the administration of hydroxycarboxylic or polybasic carboxylic acids such as citric acid, tartaric acid, fumaric acid, etc. or their salts to poultry results in improvements in egg production rate and egg quality. Moreover, Japanese Patent Laid open No. (JP-A) 56-121436 discloses a formula feed comprising a milk replacer supplemented with C.sub.4-6 carboxylic acids or salts thereof for improved palatability and accelerated growth of calves.
Regarding acidic milk replacers for young calves, it has been reported that the use of an acidic milk replacer containing 0.2% of fumaric acid as added provides for free nursing, prevents diarrhea and improves growth in the fattening stage [Chiba Prefectural Livestock Center Report 13 (1989), pp. 119-121 and Chiba Prefectural Livestock Center Report 14 (1990), pp. 29-34.]
It has also been reported that supplementing a cattle ration with fumaric acid is effective in the prophylaxis and therapy of mastitis in cows [Journal Japanese Veterinarians Association 39 (Supplemental Issue) (1985)].
Meanwhile, roughages and concentrates have been used for ruminant animals having well-developed rumination systems, such as dairy and feeder cattle. Chemical decomposition of the feed taken into the rumen of such a ruminant animal occurs anaerobically in the presence of enzymes provided by both the animal and the bacterial and protozoan symbionts in its rumen and the carbohydrates metabolized by microorganisms within the rumen are finally converted to volatile fatty acids (VFA) such as acetic acid, propionic acid, butyric acid, etc., carbon dioxide and methane. The VFA mentioned above is absorbed chiefly from the rumen. Furthermore, in the rumen, the feed is partially decomposed and the microorganisms, their cell components and undecomposed feed components find their way into the abomasum and, thence, into the small intestine. In this small intestine the cell components are digested by secreted enzymes and the products of digestion are absorbed from the bowels. Moreover, said VFA maintains the gastric juice in the rumen normally at pH about 5.5 to 6.5.
When the absorption of acetic acid and propionic acid, among species of said VFA, is encouraged, the synthesis of fat in the body is enhanced that the milk secretions may have an increased milk fat percentage. Increased absorption of acetic acid encourages the increase of fat and, hence, improves the quality of meat and produces a high quality meat such as marbled beef. Therefore, in order to insure an increased milk production and a favorable body weight gain and further to improve the degree of marbling positively with good reproducibility, it is beneficial to supply lactating cows or feeders with a concentrate ration well-designed taking their nutrient requirements into consideration. Particularly for the cows having a high production history or those bred under unfavorable climatic conditions, in which deficiencies in milk protein and fat are apt to appear, it is advantageous to supply a concentrate to enhance the production of acetic acid and propionic acid among various species of VFA.
However, when a ruminant with a well-developed rumination system is supplied with large quantities of a concentrate, foaming in the rumen is invigorated to increase chances for frothy flatulence, or foamy bloat, and tend to make the pH of the rumen fluid unstable. Particularly the supply of a concentrate in large amounts lowers the proportion of acetic acid in the total VFA. Therefore, there is an inherent limit to enhancement of the efficiency of milk and meat production or of the quality of meat.
On the other hand, the supply of a formula feed rich in roughage and having a high cellulose results in the production of an assortment of acids in which acetic acid is predominant and, moreover, a low rate of cellulose digestion. Therefore, when a ration containing both a roughage and a concentrate is employed, the ruminant animal cannot utilize the feed effectively so that its milk or meat productivity is decreased.
Meanwhile, it is described in Japanese Patent Publication No. (JP-B) 3-31422 that the use of an acidic milk replacer containing an acid (e.g. fumaric acid) finely divided to 100 mesh pass as a supplement for young cattle and other young animals helped to prevent the agglutination and coagulation of milk protein.
However, feeding a ruminant having a well-developed rumination system with an acid finely divided to 100 mesh pass results in a rapid dissolution of the acid in the rumen and, moreover, detracts from the palatability of the ration. And the resultant decrease in food intake makes it difficult to enhance the efficiency of milk or meat production.